English
There is a graded multiplication on the tensor product of graded algebras that is bilinear and compatible with the grading, described by a certain universal construction.
Русский
Существует градуированное умножение на тензорном произведении градуированных алгебр, би-линейное и совместимое с градацией, задаваемое универсальным образом.
LaTeX
$$$$ gradedMul_R(\mathcal{A},\mathcal{B}): (\bigoplus_i \mathcal{A}_i) \otimes_R (\bigoplus_j \mathcal{B}_j) \to (\bigoplus_k \mathcal{A}_k) \otimes_R (\bigoplus_l \mathcal{B}_l) $$$$
Lean4
/-- The multiplication operation for tensor products of externally `ι`-graded algebras. -/
noncomputable def gradedMul :=
val_proj @wrapped✝.{}